If you’re going to view the total solar eclipse on Aug. 21, you will need to protect your eyes, and here’s why.
Your eye acts like a magnifying glass, focusing light onto your retina, light-sensitive tissue made up of rods and cone photoreceptors in the back of your eyeball. If you were to stare into the sun for more than just a few seconds, you would burn a crater in your retina, much like holding up a magnifying glass on a sunny day and burning holes in leaves or paper.
Of course, if exposed to a bright light, our natural aversion response kicks in, and we quickly squint our eyes and look away. This is especially noticeable while driving on a dark road at night when your iris increases the diameter of your pupil to let in as much light as possible, much like the f-stop control that either opens or closes the aperture on a camera lens. In conditions like this, approaching cars, with their high beams on, can blind you.
Wide-open pupils are one of the reasons that viewing a solar eclipse can be dangerous. As the secondary shadow called the penumbra (when the moon only covers part of the sun) moves over your area, it gets darker. As the moon blocks more and more of the sun’s light, your pupils naturally become larger, letting in more electromagnetic spectrum energy and increasing the chances for an eye injury, especially in areas with higher sun blockage. A few folks undoubtedly will be so determined to see this eclipse without proper protective equipment, they will suppress their natural aversion response and look directly at the partial eclipse – a bad idea indeed.
To view the eclipse directly, use approved solar filters or No. 14 welder’s goggles. Welder’s glasses are numbered from 1 to 14; No. 14 is the only one dark enough for safe solar viewing. You also can project the image. Get a piece of cardboard, punch a pin hole in it, and then angle the cardboard to project the sun’s light on another piece of cardboard or another flat object.
The only safe time to remove your eye protection and enjoy one of the greatest natural spectacles afforded to us is when you are in the band of the totality of a total eclipse.
Due to the earth’s spherical shape, the 60- to 70-mile-wide umbra will sprint eastward across a swath from Oregon to South Carolina at 2,900 mph at the West Coast, slowing to 1,500 mph by the time it reaches the East Coast.
For most of us, the total eclipse will last a little over two minutes. However, I’ve noticed that a few chartered aircraft companies, along with Alaska Airlines, are offering solar eclipse flights that will take you above the clouds for near perfect viewing. Along the East Coast, corporate jets flying at high altitudes and nearly the speed of sound can extend the display time of totality by several minutes. In fact, NASA is going the chase the moon’s shadow with a pair half century old reconnaissance aircraft, the WB-57F Canberra, that fly to 70,000 feet. From these aircraft, the eclipse is expected to last over seven minutes.
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I will be speaking to the Arroyo Grande Lions Club on the impacts of climate change on our local weather at 7 p.m. Wednesday at the Arroyo Grande Community Center, 211 Vernon St., Arroyo Grande. I would love to see you there.
John Lindsey’s column is special to The Tribune. He is PG&E’s Diablo Canyon marine meteorologist and a media relations representative. Email him at email@example.com or follow him on Twitter @PGE_John.